7 Segment LED Board

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This is a serially-interfaced 7 segment LED kit which can be linked together to create numerical displays.

The LED display is a large 45mm/1.75″ unit with super-bright LEDs and is easily daylight visible.

The board contains a shift register and a power stage to control the display.

This can be controlled via a microcontroller – with Arduino examples included here.

Here at Renewable Energy Innovation we have been asked to provide large visible displays, mainly to show power and energy. These are generally run form 12V DC supplies. In fact we have been asked to do it so many times, that I thought I would design a relatively simple LED display unit which can be wired together to create large numerical displays. So here it is. The kit is available from us, via the links here. Or here are full instructions for you to build your own.

Instructions

Design Overview

This board is a relatively simple design. Each of the 7 segments of the LED is controlled by one bit of a shift register. The decimal point is also controlled by the shift register. This means each board is controlled via an 8 bit binary number.

Data is moved into the shift register serially (check the example code for more details). The LATCH pin is taken LOW. Serial data is then moved into the shift register by first setting the DATA line to 0 or 1, then pulsing the CLOCK line. When 8 bits have been shifted in then the LATCH pin is taken high and the output displays whatever values are in the register.

The output from the shift register is just 5V, which is not enough to drive the large 7 segment LED display. This requires 12V and curent limiting resistors (330 ohm for 12V). A UN2003 7 transistor array is used to control each of the 7 segments. These transistors control the low side of the device. The 7 segment display must be a common-anode type.

The decimal point is a special cas as it only contains one LED, hence must have a different current limit. An additioanl NPN transistor is used along with a 1k current limiting resistor to control the decimal point.

If you have more than one board in series (they are designed to fit together to make large numerical displays), then you need to clock in all the data to control every part of the display. For example – if we have three digits then we must clock in three 8-bit digital numbers and then set the LATCH high. This will then control all three digits.

Check out the instructions and the exmple code for more information.

The device is wired with the following connectors (P1 (input) and P2 (output) are as follows):

Hey Paul,
Its been a long time!
Yep – this could definitely be used with the Paspberry Pi.
It should just be a matter of using 3 of the digital GPIO on the RPi, potentially with something like WiringPi (http://wiringpi.com/).

I might have a quick go at wiring that up as it might be useful to folk.
Cheers for the comment. Hope its all going good for you,

Matt

Quoting Guest:Looks good Matt!

I wonder if you could get it to work with a Raspberry Pi as the controller? I expect its possible and might be a cheaper alternative…

Quoting Guest:Great board – I would like to make a 4-digit clock with these, but haven’t the microcontroller skills to do it myself. Do you know of any ready-made clock driver?
Thanks,
Richard.

Hi Richard, I am afraid I dont know of any ready-made clock unit that would work ‘out of the box’ with this display – you would need a real time clock module to give you a timestamp and a microcontroller (I generally use the Arduino bootloader) to read the real time clock and display the time on the display.

Hi Theo,
Yep – you can easily put 9 units in a row ans they would all be controlled by just three digital lines. You would clock in the data to all 9 units and thn set the latch line and the data would be isplayed. This can be done very fast so numbers can be upated regularly. Check out SerialOut function in Arduino IDE.

Let me know if you are interested – I can sort out a better price for 9 units.

Hi thank you so much.
Do you also have the common cathod driver board? Does this board also support the 2.3″ seven segment displays as there are other holes that are wider than the one that you are using?

Hi, Thanks for your comment.
I am afraid that, while the 7 segment LED board has pins to connect to the larger 2.3″ LED units (designed for Kingbright SA23-12EWA), it only works for common annode connection. So this board would not work for common cathode displays.
Let me know if you need any more info.
Regards,

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